A Uterus‐Inspired Niche Drives Blastocyst Development to the Early Organogenesis

Abstract The fundamental physical features such as the mechanical properties and microstructures of the uterus need to be considered when building in vitro culture platforms to mimic the uterus for embryo implantation and further development but have long been neglected. Here, a uterus‐inspired niche (UN) constructed by grafting collagen gels onto polydimethylsiloxane based on a systematic investigation of a series of parameters (varying concentrations and thicknesses of collagen gel) is established to intrinsically specify and simulate the mechanics and microstructures of the mouse uterus. This brand‐new and unique system is robust in supporting embryo invasion, as evidenced by the special interaction between the embryos and the UN system and successfully promoting E3.5 embryo development into the early organogenesis stage. This platform serves as a powerful tool for developmental biology and tissue engineering.


Supplementary notes Previous studies on embryo culture and embryo-material interactions
The first mouse blastocyst cultured in vitro was reported by being injected into the fiber network of the bovine eye. [1] Currently, the typical dishes used for embryo culture are made of polystyrene, silicone, or specialized plastic polymer-coated with collagen, laminin, fibrinogen, or some other matrix [2][3][4][5][6] and the embryos exhibited limited developmental potency.
The cell microenvironment, a complicated and dynamic biochemical and physical environment, can control cell behaviors and development and determine cell fates. [7] An embryo, which is a well-organized cell cluster, is also sensitive to the surrounding conditions. [8,9] 3D biomaterial systems have provided a paradigm shift in cell culture in vitro, and considerable research efforts have been devoted to material properties, including macro/nanostructure, elasticity, stiffness, and micro/nanopatterns that influence cell states [10][11][12][13][14] through chemical pathways. [15][16][17][18][19][20] Our UN platform was established according to a good understanding of the structure of the uterus and developmental biology. Developing an appropriate culture method in vitro is crucial to exploring the black box of embryo development and stem cell-based embryo assembly, which has attracted much attention. [6,[21][22][23][24][25][26][27][28][29] To the best of our knowledge, the UN system not only extends the embryo culture period from the initial blastocyst stage to the heartbeat-like stage but also reveals molecular regulators between materials and embryos, which govern cell migration, to regulate embryo spreading and developmental potential. [30][31][32][33][34][35] Table S1. TE, trophectoderm; PrE, primitive endoderm; pre-EPI, epiblast at preimplantation stage; EPI, epiblast.     Bonferroni post hoc test. ns, no significance; ns, P > 0.05; *P < 0.05; **P < 0.01.

Movie S1
The movie of representative stress-strain curve for uniaxial tensile test of the uterus. During the tensile test, the strain gradually increased (left panel) when the uterine sample was slowly stretched upward (right panel). The points on the stress-strain curve referred to the motion when the sample was stretched from the tensile test loading cell.

Movie S2
The

Movie S7
One embryo with a heartbeat-like beating cultured on PDCO after approximately 8 days of in vitro culture and zooming into the beating site through magnification.